A variety of reactors has been used to process semiconductor substrates. Typically, each reactor 100 included a reaction chamber 105 within which a susceptor 107 was mounted. Susceptor 107 supported one of more substrates 190.
To improve process uniformity, typically, susceptor 107 was rotated by a rotation assembly that included pulleys 127, 128, and motor 123. Those of skill in the art will appreciate that reactor 100 includes several other components. However, herein, only the components necessary to understand the limitations of prior art reactor 100 are considered.
For reactor 100, a shaft 110 was part of susceptor 107. To mount susceptor 107 in reaction chamber 105, dome top 109 was removed from base 125. Shaft 110 of susceptor 107 was placed in a slip-fit bore 115 of a spindle 113.
Spindle 113 extended through reaction chamber 105 and was connected to a pulley 128 outside of reaction chamber 105. Pulley 128 was driven by another pulley 127, which in turn was driven by stepper motor 123.
Normally, susceptor 107 assumed two positions, a lower wafer load position and an elevated wafer processing position. In FIG. 1, the dashed lines within reaction chamber 105 show the substrate processing position of susceptor 107 while the solid lines show the substrate load position.
One problem with reactor 100 was the coupling between spindle 113 and shaft 110. To permit shaft 110 to fit inside bore 115, bore 115 had a slightly larger diameter than a diameter of shaft 110. The resulting small clearance between shaft 110 and bore 115 allowed susceptor 107 to move about within bore 115 as susceptor 107 was rotated during processing.
The movement within bore 115 resulted in a wobble of susceptor 107. The wobble was most accentuated at the periphery of susceptor 107 and resulted in poor epitaxial characteristics.
The wobble of susceptor 107 also resulted in wearing of susceptor shaft 110 which in turn increased the clearance and resulted in a more severe wobble. Reactor 100 was stopped for maintenance when the movement of the susceptor associated with the wobble exceeded a predetermined limit.
To improve the quality of the epitaxial deposition and to reduce maintenance, there is a need to effectively eliminate susceptor wobble while keeping the installation and removal of susceptor 107 reasonably easy.